Wireless communication systems are well known in which mobile units can initiate or receive calls while roaming between different radio frequency (RF) coverage areas (sometimes referred to as “cells”). The mobile units communicate via RF resources with base stations distributed among the cells, which base stations are controlled by one or more mobile switching centers (MSCs). The MSCs provide control signaling for the call and connect the mobile unit to other participating endpoints, which may comprise other mobile units or wireline units.
Occasionally, mobile units can encounter periodic service interruption(s) during a call, for example, upon entering a tunnel or reaching a fringe RF coverage area or due to a handoff error, causing the mobile unit to become dropped (at least temporarily) from the call. In such case, network-initiated reconnect attempts are known whereby the MSC attempts to page the mobile unit to find its location, reconnect the mobile unit and preserve the call. However, network-initiated reconnects can be wasteful in terms of network resources and bandwidth, most particularly when there are multiple dropped calls and hence multiple pages flooding the network. An alternative manner of reconnect, called a mobile-originated reconnect, is disclosed in related patent application Ser. No. 10/761,067. In the mobile-originated reconnect, the mobile unit itself initiates reconnect of a call by sending a mobile-originated reconnect (MORC) message to the network. Alter receiving the MORC message, the network attempts to identify a suspended communication session involving the mobile unit and, if a suspended session is so identified within a designated time, the network performs reconnection of the call. In such manner, the suspended session becomes reconnected without relying on network paging.
A problem that affects both of the above reconnect approaches is that mobile unit(s) may roam between base station sites controlled by different MSCs during the service interruption (as would occur, for example, when mobile units roam between different communication systems). This is known as a border cell problem. In the case of network-initiated reconnects, movement of the mobile unit to a border cell inhibits the ability of the serving MSC to page the mobile unit and reconnect the call. Indeed, the page may never be received if the mobile unit moves away from the area of the serving MSC. Further, a mobile unit may hear a page from one base station and respond to another base station controlled by a different MSC. In the case of mobile-originated reconnects, movement of the mobile unit to a border cell may cause MORC messages to be received at a border MSC that has no record of the suspended communication session while, at the same time, the serving MSC (i.e., the MSC having a record of the suspended communication) expects but does not receive a MORC message. The net effect of unsuccessful reconnection is a decreased revenue stream for the service provider.
Accordingly, there is a need for methods to accommodate reconnection of wireless calls to mobile units in border cell situations, wherein mobile units have roamed to border cells controlled by border MSCs. Advantageously, the methods will support both network-initiated and mobile-originated reconnect approaches. The present invention is directed to addressing these needs.